Preparation of sulfide chain-bearing organosilicon compounds

ABSTRACT

By premixing a sulfide chain-bearing organosilicon compound, a halogenoalkyl group-bearing organosilicon compound, and optionally, sulfur, adding anhydrous sodium sulfide Na 2 S to the premix, and allowing reaction to take place, a sulfide chain-bearing organosilicon compound having a shorter sulfide chain can be prepared in high yields and at a lost cost while minimizing formation of monosulfide-bearing organosilicon compound.

FIELD OF THE INVENTION

[0001] This invention relates to a method for changing the sulfide chaindistribution of a sulfide chain-bearing organosilicon compound havingthe following general formula (1):

(R¹O)_((3−p))(R²)_(p)Si—R³—S_(m)—R³—Si(OR¹)_((3−p))(R²)_(p)  (1)

[0002] wherein R¹ and R² each are a monovalent hydrocarbon group having1 to 4 carbon atoms, R³ is a divalent hydrocarbon group having 1 to 10carbon atoms, m has an average value of 2<m≦6, and p is 0, 1 or 2. Moreparticularly, it relates to a method for converting a sulfidechain-bearing organosilicon compound having the formula (1) to a sulfidechain-bearing organosilicon compound having a shorter sulfide chain in adistribution having a minimized content of monosulfide-bearingorganosilicon compound.

BACKGROUND OF THE INVENTION

[0003] In silica-loaded tires, bis-triethoxysilyltetrasulfide is widelyused as a coupling agent between rubber and silica. However, when mixedwith rubber and silica at elevated temperatures, this compound acts toincrease the viscosity of the blend, which is inconvenient to subsequentoperation.

[0004] To overcome this problem, shorter chain polysulfide compoundssuch as bis-triethoxysilylpropyldisulfide were proposed. For example,JP-A 9-169774 discloses a method for preparing disulfide silanes usingNaCN. This method, however, has the problem of using the toxic compound.It would be desirable to have a substitute safe method of preparingshort sulfide chain-bearing organosilicon compounds at low cost.

[0005] The inventors proposed in JP-A 11-100388 a method of preparing ashort sulfide chain-bearing organosilicon compound by reacting apolysulfide silane of the general formula: (RO)₃SiC₃H₆S_(x)C₃H₆Si(OR)₃wherein R is methyl or ethyl, and x is a positive number of 3 to 6 onthe average, at least one anhydrous sulfur compound: M¹ ₂S or M²Swherein M¹ is an alkali metal or ammonium and M² is an alkaline earthmetal or zinc, and a halogenoalkoxysilane of the general formula:XC₃H₆Si(OR)₃ wherein X is halogen and R is methyl or ethyl. When theshort sulfide chain-bearing organosilicon compound is prepared by thismethod, however, there can also be produced a monosulfide chain-bearingorganosilicon compound, that is, an organosilicon compound having asulfide chain which does not fully participate in the reactions withsilica and rubber.

SUMMARY OF THE INVENTION

[0006] An object of the present invention is to provide a safe andeconomical method for preparing, from a sulfide chain-bearingorganosilicon compound of the formula (1), a sulfide chain-bearingorganosilicon compound having a shorter average sulfide chain and havinga minimal content of monosulfide chain-bearing organosilicon compound inits composition.

[0007] In one aspect, the present invention provides a method forpreparing a sulfide chain-bearing organosilicon compound, comprising thesteps of:

[0008] premixing a sulfide chain-bearing organosilicon compound havingthe general formula (1):

(R¹O)_((3−p))(R²)_(p)Si—R³—S_(m)—R³—Si(OR¹)_((3−p))(R²)_(p)  (1)

[0009] wherein R¹ and R² each are a monovalent hydrocarbon group of 1 to4 carbon atoms, R³ is a divalent hydrocarbon group of 1 to 10 carbonatoms, m has an average value of 2<m≦6, and p is 0, 1 or 2, ahalogenoalkyl group-bearing organosilicon compound having the generalformula (2):

(R¹O)_((3−p))(R²)_(p)Si—R³—X  (2)

[0010] wherein R¹ and R² each are a monovalent hydrocarbon group of 1 to4 carbon atoms, R³ is a divalent hydrocarbon group of 1 to 10 carbonatoms, X is a halogen atom, and p is 0, 1 or 2, and optionally, sulfur,

[0011] adding anhydrous sodium sulfide represented by Na₂S to thepremix, and

[0012] allowing reaction to take place for thereby forming a sulfidechain-bearing organosilicon compound having the general formula (3):

(R¹O)_((3−p))(R²)_(p)Si—R³—S_(n)—R³—Si(OR¹)_((3−p))(R²)_(p)  (3)

[0013] wherein R¹ and R² each are a monovalent hydrocarbon group of 1 to4 carbon atoms, R³ is a divalent hydrocarbon group of 1 to 10 carbonatoms, n has an average value of 2≦n<6, satisfying m>n, and p is 0, 1 or2, while minimizing formation of a monosulfide-bearing organosiliconcompound with n=1.

[0014] In another aspect, the present invention provides a method forpreparing a sulfide chain-bearing organosilicon compound, comprising thesteps of:

[0015] preforming a sulfide chain-bearing organosilicon compound havingthe general formula (1):

(R¹O)_((3−p))(R²)_(p)Si—R³—S_(m)—R³—Si(OR¹)_((3−p))(R²)_(p)  (1)

[0016] wherein R¹ and R² each are a monovalent hydrocarbon group of 1 to4 carbon atoms, R³ is a divalent hydrocarbon group of 1 to 10 carbonatoms, m has an average value of 2<m≦6, and p is 0, 1 or 2, fromanhydrous sodium sulfide represented by Na₂S, sulfur, and ahalogenoalkyl group-bearing organosilicon compound having the generalformula (2):

(R¹O)_((3−p))(R²)_(p)Si—R³—X  (2)

[0017] wherein R¹ and R² each are a monovalent hydrocarbon group of 1 to4 carbon atoms, R³ is a divalent hydrocarbon group of 1 to 10 carbonatoms, X is a halogen atom, and p is 0, 1 or 2,

[0018] if necessary, combining the sulfide chain-bearing organosiliconcompound of formula (1) with the halogenoalkyl group-bearingorganosilicon compound of formula (2) and optionally, sulfur,

[0019] adding anhydrous sodium sulfide represented by Na₂S to thesulfide chain-bearing organosilicon compound of formula (1), and

[0020] allowing reaction to take place for thereby forming a sulfidechain-bearing organosilicon compound having the general formula (3):

(R¹O)_((3−p))(R²)_(p)Si—R³—S_(n)—R³—Si(OR¹)_((3−p))(R²)_(p)  (3)

[0021] wherein R¹ and R² each are a monovalent hydrocarbon group of 1 to4 carbon atoms, R³ is a divalent hydrocarbon group of 1 to 10 carbonatoms, n has an average value of 2≦n<6, satisfying m>n, and p is 0, 1 or2, while minimizing formation of a monosulfide-bearing organosiliconcompound with n=1.

[0022] With this method, the desired sulfide chain-bearing organosiliconcompound, and especially a sulfide chain-bearing organosilicon compoundof formula (3) wherein n has an average value of 2 to 3 is produced inhigh yields while minimizing the content of monosulfide-bearingorganosilicon compound of formula (3) wherein n=1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Briefly stated, according to the invention, by premixing asulfide chain-bearing organosilicon compound of formula (1), ahalogenoalkyl group-bearing organosilicon compound of formula (2), andoptionally, sulfur, adding anhydrous sodium sulfide represented by Na₂Sthereto, and allowing reaction to take place, a sulfide chain-bearingorganosilicon compound of formula (3) is obtained while minimizingformation of monosulfide-bearing organosilicon compound of formula (3)wherein n=1.

[0024] One starting reactant is a sulfide chain-bearing organosiliconcompound having the average compositional formula (1).

(R¹O)_((3−p))(R²)_(p)Si—R³—S_(m)—R³—Si(OR¹)_((3−p))(R²)_(p)  (1)

[0025] In the formula, R¹ and R² are independently selected frommonovalent hydrocarbon groups having 1 to 4 carbon atoms, for example,alkyl and alkenyl groups such as methyl, ethyl, n-propyl, i-propyl,n-butyl, i-butyl, t-butyl, allyl and methallyl. R³ is selected fromdivalent hydrocarbon groups having 1 to 10 carbon atoms, for example,alkylene, arylene and alkenylene groups and combinations thereof, suchas methylene, ethylene, propylene, n-butylene, i-butylene, hexylene,decylene, phenylene, and methylphenylethylene, and combinations thereof.The subscript m has an average value of 2<m≦6 and preferably 3≦m≦4, andp is equal to 0, 1 or 2, preferably 0 or 1, most preferably 0.

[0026] Typical examples of the compound of formula (1) are given below.

(CH₃O)₃Si—(CH₂)₃—S_(m)—(CH₂)₃—Si(OCH₃)₃

(CH₃CH₂O)₃Si—(CH₂)₃—S_(m)—(CH₂)₃—Si(OCH₂CH₃)₃

(CH₃CH₂O)₃Si—CH₂CH(CH₃)CH₂—S_(m)—CH₂CH(CH₃)CH₂—Si(OCH₂CH₃)₃

[0027] In the above-described compounds, S has a distribution partiallybecause of disproportionation reaction, so that its number (m) isdescribed essentially as an average value. In formula (1), m has anaverage value of 2<m≦6 and preferably 3≦m≦4.

[0028] The halogenoalkyl group-bearing organosilicon compound usedherein has the following general formula (2).

(R¹O)_((3−p))(R²)_(p)Si—R³—X  (2)

[0029] In the formula, R¹, R², R³ and p are as defined above, and X is ahalogen atom such as Cl, Br or I, preferably Cl or Br.

[0030] Typical examples of the compound of formula (2) are given below.

(CH₃O)₃Si—(CH₂)₃—Cl

(CH₃O)₃Si—(CH₂)₃—Br

(CH₃CH₂O)₃Si—(CH₂)₃—Cl

(CH₃CH₂O)₃Si—(CH₂)₃—Br

(CH₃CH₂O)₃Si—CH₂CH(CH₃)CH₂—Cl

[0031] When the reaction is conducted, sulfur is added if desired foradjusting the length of sulfide chain. It is not preferred to add alarge amount of sulfur because the resulting product contains moremonosulfide chain-bearing organosilicon compound.

[0032] According to the invention, the compounds of formulae (1) and (2)and optionally, sulfur are mixed, and anhydrous sodium sulfiderepresented by Na₂S is then added to the mixture whereupon reaction iscarried out.

[0033] The use of a solvent is optional when the end compound isprepared according to the invention. A solventless system is acceptable.Examples of the solvent, if used, include aliphatic hydrocarbons such aspentane, hexane, heptane and octane, aromatic hydrocarbons such asbenzene, toluene and xylene, alcohols such as methanol and ethanol, andethers such as diethyl ether, dibutyl ether, tetrahydrofuran anddioxane. Of these, the ethers such as dibutyl ether, tetrahydrofuran anddioxane and the alcohols such as methanol and ethanol are preferred.

[0034] In a preferred embodiment, the compounds of formulae (1) and (2)and optional sulfur are mixed in a solvent, and Na₂S is gradually addedto the mixture for reaction to take place; and the reaction mixture isripened following the addition of Na₂S.

[0035] The reaction temperature is not critical and generally rangesfrom room temperature to about 200° C., and preferably from about 60° C.to about 170° C. The reaction time is usually about 30 minutes or more.The reaction proceeds to completion within about 2 hours to about 15hours.

[0036] With respect to the molar ratio of the compound of averagecompositional formula (1) to Na₂S, the Na₂S may be added in accordancewith the desired value of n in the average compositional formula (3).Most often the compound of formula (2) may be added in an equimolaramount to Na in the Na₂S added. It is noted that the system becomesalkaline as the moles of the compound of formula (2) decreases, andbecomes nearly neutral as the moles of the compound of formula (2)increases. More illustratively, when reaction is made among 1 mole ofthe compound of average compositional formula (1) wherein m has anaverage value of 4, 1 mole of Na₂S and 2 moles of the compound offormula (2), there is obtained a compound of average compositionalformula (3) wherein n has an average value of 2.5. When the solvent isused, it may be distilled off in vacuum at the end of reaction andbefore or after the salt formed is separated by filtration.

[0037] The compound of average compositional formula (1) used herein maybe a previously isolated one. Alternatively, in the same reactor as usedfor the reaction, a sulfide chain-bearing organosilicon compound ofaverage compositional formula (1) is previously formed from sodiumsulfide Na₂S, sulfur, and a halogenoalkyl group-bearing organosiliconcompound of formula (2). Thereafter, the halogenoalkyl group-bearingorganosilicon compound of formula (2) and optionally, sulfur are addedand mixed therewith, if necessary, and Na₂S is added for reaction totake place whereby the sulfide chain-bearing organosilicon compound ofaverage compositional formula (3) is obtained.

[0038] In the alternative procedure, when the compound of averagecompositional formula (1) is preformed, the order of addition of Na₂S,the organosilicon compound of formula (2) and sulfur is arbitrary. Inthe step of preforming the compound of average compositional formula(1), the compound of formula (2) and sulfur may be added in amounts thatinclude their amounts to be added later.

[0039] The use of a solvent is optional when the compound of formula (1)is preformed. A solventless system is acceptable. Examples of thesolvent, if used, include aliphatic hydrocarbons such as pentane andhexane, aromatic hydrocarbons such as benzene, toluene and xylene,ethers such as tetrahydrofuran, diethyl ether and dibutyl ether, andalcohols such as methanol and ethanol. Of these, the ethers such astetrahydrofuran and the alcohols such as methanol and ethanol arepreferred.

[0040] The reaction temperature in the preforming step is not criticaland generally ranges from room temperature to about 200° C., andpreferably from about 60° C. to about 170° C. The reaction time isusually about 30 minutes or more. The reaction proceeds to completionwithin about 30 minutes to about 8 hours, allowing progress to thesubsequent reaction.

[0041] Once the compound of formula (1) is obtained through the abovereaction, Na₂S is added thereto for reaction to take place to producethe compound of formula (3) in the same way and under the sameconditions as described above.

[0042] The thus obtained compound has the average compositional formula(3).

(R¹O)_((3−p))(R²)_(p)Si—R³—S_(n)—R³—Si(OR¹)_((3−p))(R²)_(p)  (3)

[0043] In the formula, R¹ and R² each are a monovalent hydrocarbon grouphaving 1 to 4 carbon atoms, and R³ is a divalent hydrocarbon grouphaving 1 to 10 carbon atoms, examples of which are as illustrated inconjunction with formula (1). The subscript p is 0, 1 or 2. Thesubscript n has an average value of 2≦n<6, and is smaller than m informula (1), i.e., m>n, and preferably has an average value of 2≦n≦3,exclusive of m=n=3. In the compound (mixture) obtained by the inventivemethod, the formation of the compound of formula (3) wherein n=1 isminimized, to a level of at most 5 mol %, preferably at most 2 mol %,and especially at most 1 mol %.

[0044] Typical examples of the compound of formula (3) are given below.

(CH₃O)₃Si—(CH₂)₃—S_(n)—(CH₂)₃—Si(OCH₃)₃

(CH₃CH₂O)₃Si—(CH₂)₃—S_(n)—(CH₂)₃—Si(OCH₂CH₃)₃

(CH₃CH₂O)₃Si—CH₂CH(CH₃)CH₂—S_(n)—CH₂CH(CH₃)CH₂—Si(OCH₂CH₃)₃

EXAMPLE

[0045] Examples of the invention are given below by way of illustrationand not by way of limitation.

Example 1

[0046] A 1-liter separable flask equipped with a nitrogen gas inlet,thermometer, Dimroth condenser and dropping funnel was charged with 300g of ethanol, 269 g (0.5 mol) of bis-triethoxysilylpropyltetrasulfide,and 240.5 g (1.0 mol) of 3-chloropropyltriethoxysilane and heated at 70°C. To the flask, 39 g (0.5 mol) of anhydrous sodium sulfide wasgradually added over 10 minutes. At the end of addition, the reactionmixture was ripened for 8 hours. The solution was then filtered. Thefiltrate was concentrated in vacuum in a rotary evaporator, yielding 437g of a brown clear liquid. On analysis by infrared (IR) absorptionspectroscopy and proton nuclear magnetic resonance (¹H-NMR) spectroscopyand sulfur content determination, it was confirmed to be a sulfidegroup-bearing alkoxysilane of the following average compositionalformula.

(CH₃CH₂O)₃Si(CH₂)₃—S_(2.5)—(CH₂)₃Si(OCH₂CH₃)₃

[0047] To confirm the sulfide distribution of the compound,supercritical chromatography was carried out. Its sulfide silanedistribution (mol %) is shown below. n = 1 0.5% n = 2 56.6% n = 3 30.5%n = 4 10.3% n = 5 2.1% n = 6 ≦0.1%

[0048] The bis-triethoxysilylpropyltetrasulfide used as the startingreactant had the sulfide silane distribution (mol %) shown below. m = 10.1% m = 2 18.7% m = 3 30.3% m = 4 24.6% m = 5 16.1% m = 6 6.2% m = 73.1% m = 8 1.0%

Example 2

[0049] A 2-liter separable flask equipped with a nitrogen gas inlet,thermometer, Dimroth condenser and dropping funnel was charged with 500g of ethanol, 39 g (0.5 mol) of anhydrous sodium sulfide, and 48 g (1.5mol) of sulfur and heated at 70° C. To the flask, 240.5 g (1.0 mol) of3-chloropropyltriethoxysilane was slowly added dropwise over 30 minutes.At the end of addition, the reaction mixture was ripened for 2 hours.The solution was cooled to 35° C., and 240.5 g (1.0 mol) of3-chloropropyltriethoxysilane was added thereto. The solution was heatedat 70° C., after which 39 g (0.5 mol) of anhydrous sodium sulfide wasgradually added over 10 minutes. At the end of addition, the reactionmixture was ripened for 8 hours. The solution was then filtered. Thefiltrate was concentrated in vacuum in a rotary evaporator, yielding 433g of a brown clear liquid. On analysis by IR and ¹H-NMR spectroscopy andsulfur content determination, it was confirmed to be a sulfidegroup-bearing alkoxysilane of the following average compositionalformula, as in Example 1.

(CH₃CH₂O)₃Si(CH₂)₃—S_(2.5)—(CH₂)₃Si(OCH₂CH₃)₃

[0050] To confirm the sulfide distribution of the compound,supercritical chromatography was carried out. Its sulfide silanedistribution (mol %) is shown below. n = 1 0.7% n = 2 55.4% n = 3 31.5%n = 4 10.4% n = 5 2.0% n = 6 ≦0.1%

Example 3

[0051] A 2-liter separable flask equipped with a nitrogen gas inlet,thermometer, Dimroth condenser and dropping funnel was charged with 500g of ethanol, 39 g (0.5 mol) of anhydrous sodium sulfide, and 40.0 g(1.25 mol) of sulfur and heated at 70° C. To the flask, 481.0 g (2.0mol) of 3-chloropropyltriethoxysilane was slowly added dropwise over 45minutes. At the end of addition, the reaction mixture was ripened for 2hours. To the solution, 39 g (0.5 mol) of anhydrous sodium sulfide wasgradually added over 10 minutes. At the end of addition, the reactionmixture was ripened for 8 hours. The solution was then filtered. Thefiltrate was concentrated in vacuum in a rotary evaporator, yielding 448g of a brown clear liquid. On analysis by IR and ¹H-NMR spectroscopy andsulfur content determination, it was confirmed to be a sulfidegroup-bearing alkoxysilane of the following average compositionalformula.

(CH₃CH₂O)₃Si( CH₂)₃—S_(2.25)—(CH₂)₃Si(OCH₂CH₃)₃

[0052] To confirm the sulfide distribution of the compound,supercritical chromatography was carried out. Its sulfide silanedistribution (mol %) is shown below. n = 1 0.7% n = 2 71.5% n = 3 22.7%n = 4 4.2% n = 5 0.9% n = 6 ≦0.1%

Comparative Example 1

[0053] A 2-liter separable flask equipped with a nitrogen gas inlet,thermometer, Dimroth condenser and dropping funnel was charged with 300g of ethanol, 269 g (0.5 mol) of bis-triethoxysilylpropyltetrasulfide,and 39.0 g (0.5 mol) of anhydrous sodium sulfide. Reaction was conductedat 80° C. for 1 hour. Thereafter, 240.5 g (1.0 mol) of3-chloropropyltriethoxysilane was added dropwise over 30 minutes. Afterthe completion of dropwise addition, the reaction solution was ripenedfor 8 hours. The solution was filtered. The filtrate was concentrated invacuum in a rotary evaporator, yielding 434 g of a brown clear liquid.On analysis by IR and ¹H-NMR spectroscopy and sulfur contentdetermination, it was confirmed to be a sulfide group-bearingalkoxysilane of the following average compositional formula, as inExample 1.

(CH₃CH₂O)₃Si(CH₂)₃—S_(2.5)—(CH₂)₃Si(OCH₂CH₃)₃

[0054] To confirm the sulfide distribution of the compound,supercritical chromatography was carried out. Its sulfide silanedistribution (mol %) is shown below. n = 1 2.1% n = 2 55.4% n = 3 29.8%n = 4 10.2% n = 5 2.5% n = 6 ≦0.1%

Comparative Example 2

[0055] A 2-liter separable flask equipped with a nitrogen gas inlet,thermometer, Dimroth condenser and dropping funnel was charged with 500g of ethanol, 78 g (1.0 mol) of anhydrous sodium sulfide and 40.0 g(1.25 mol) of sulfur and heated at 70° C. Reaction was conducted for 1hour. Thereafter, 481.0 g (2.0 mol) of 3-chloropropyltriethoxysilane wasslowly added dropwise over 45 minutes. After the completion of dropwiseaddition, the reaction solution was ripened for 8 hours. The solutionwas filtered. The filtrate was concentrated in vacuum in a rotaryevaporator, yielding 440 g of a brown clear liquid. On analysis by IRand ¹H-NMR spectroscopy and sulfur content determination, it wasconfirmed to be a sulfide group-bearing alkoxysilane of the followingaverage compositional formula, as in Example 3.

(CH₃CH₂O)₃Si(CH₂)₃—S_(2.25)—(CH₂)₃Si(OCH₂CH₃)₃

[0056] To confirm the sulfide distribution of the compound,supercritical chromatography was carried out. Its sulfide silanedistribution (mol %) is shown below. n = 1 7.3% n = 2 60.8% n = 3 24.1%n = 4 6.4% n = 5 1.4% n = 6 ≦0.1%

[0057] According to the invention, from a sulfide chain-bearingorganosilicon compound of the formula (1), a polysulfidesilane having ashorter polysulfide chain can be prepared in high yields and at a lowcost. The resulting compound is of a composition having a low content ofmonosulfide chain-bearing organosilicon compound which is less reactivewith rubber, and thus useful in the industry, typically as additives tosilica-loaded tire rubber compositions.

[0058] Japanese Patent Application No. 2002-062900 is incorporatedherein by reference.

[0059] Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A method for preparing a sulfide chain-bearing organosiliconcompound, comprising the steps of: premixing a sulfide chain-bearingorganosilicon compound having the general formula (1):(R¹O)_((3−p))(R²)_(p)Si—R³—S_(m)—R³—Si(OR¹)_((3−p))(R²)_(p)  (1) whereinR¹ and R² each are a monovalent hydrocarbon group of 1 to 4 carbonatoms, R³ is a divalent hydrocarbon group of 1 to 10 carbon atoms, m hasan average value of 2<m≦6, and p is 0, 1 or 2, a halogenoalkylgroup-bearing organosilicon compound having the general formula (2):(R¹O)_((3−p))(R²)_(p)Si—R³—X  (2) wherein R¹ and R² each are amonovalent hydrocarbon group of 1 to 4 carbon atoms, R³ is a divalenthydrocarbon group of 1 to 10 carbon atoms, X is a halogen atom, and p is0, 1 or 2, and optionally, sulfur, adding anhydrous sodium sulfiderepresented by Na₂S to the premix, and allowing reaction to take placefor thereby forming a sulfide chain-bearing organosilicon compoundhaving the general formula (3):(R¹O)_((3−p))(R²)_(p)Si—R³—S_(n)—R³—Si(OR¹)_((3−p))(R²)_(p)  (3)whereinR¹ and R² each are a monovalent hydrocarbon group of 1 to 4 carbonatoms, R³ is a divalent hydrocarbon group of 1 to 10 carbon atoms, n hasan average value of 2≦n<6, satisfying m>n, and p is 0, 1 or 2, whileminimizing formation of a monosulfide-bearing organosilicon compoundwith n=1.
 2. A method for preparing a sulfide chain-bearingorganosilicon compound, comprising the steps of: preforming a sulfidechain-bearing organosilicon compound having the general formula (1):(R¹O)_((3−p))(R²)_(p)Si—R³—S_(m)—R³—Si(OR¹)_((3−p))(R²)_(p)  (1)whereinR¹ and R² each are a monovalent hydrocarbon group of 1 to 4 carbonatoms, R³ is a divalent hydrocarbon group of 1 to 10 carbon atoms, m hasan average value of 2<m≦6, and p is 0, 1 or 2, from anhydrous sodiumsulfide represented by Na₂S, sulfur, and a halogenoalkyl group-bearingorganosilicon compound having the general formula (2):(R¹O)_((3−p))(R²)_(p)Si—R³—X  (2)wherein R¹ and R² each are a monovalenthydrocarbon group of 1 to 4 carbon atoms, R³ is a divalent hydrocarbongroup of 1 to 10 carbon atoms, X is a halogen atom, and p is 0, 1 or 2,if necessary, combining the sulfide chain-bearing organosilicon compoundof formula (1) with the halogenoalkyl group-bearing organosiliconcompound of formula (2) and optionally, sulfur, adding anhydrous sodiumsulfide represented by Na₂S to the sulfide chain-bearing organosiliconcompound of formula (1), and allowing reaction to take place for therebyforming a sulfide chain-bearing organosilicon compound having thegeneral formula (3):(R¹O)_((3−p))(R²)_(p)Si—R³—S_(n)—R³—Si(OR¹)_((3−p))(R²)_(p)  (3)whereinR¹ and R² each are a monovalent hydrocarbon group of 1 to 4 carbonatoms, R³ is a divalent hydrocarbon group of 1 to 10 carbon atoms, n hasan average value of 2≦n<6, satisfying m>n, and p is 0, 1 or 2, whileminimizing formation of a monosulfide-bearing organosilicon compoundwith n=1.
 3. The method of claim 1 wherein using a sulfide chain-bearingorganosilicon compound of formula (1) wherein m has an average value of3 to 4, a sulfide chain-bearing organosilicon compound of formula (3)wherein n has an average value of 2 to 3, exclusive of m=n=3, isobtained.